This invention relates to an apparatus and method for the placement elements on a surface, and in particular, but not exclusively to an apparatus and method for placing solder balls and flux droplets on a ball grid array (BGA) substrate in the mounting process of integrated circuit components.
BGA techniques have become more common in recent years for connecting high-density IC components onto circuit boards. A regular array of fluxed solder balls is deposited on the circuit board at points where the leads of an IC component may be desired to be connected. An IC component may then be mounted on the board and connections are made between the leads of the component and the solder balls contacted by those leads.
To achieve this end, in a ball grid array technique droplets of flux and solder balls must be transferred to a substrate where they are deposited in a predetermined array. A common technique is to use a ball pick head. The ball pick head is used for transferring the solder balls to the substrate and is designed to carry the balls in the same array configuration as is required on the substrate and then subsequently to deposit the balls on the substrate. It is important, indeed essential, that all locations on the circuit board intended to be provided with a solder ball are so provided, since otherwise if a solder ball is missing a IC component lead may not be properly connected to the board and the entire circuit board may be useless. Conventionally the ball pick head is formed with a plurality of locations for receiving solder balls, these locations being disposed in the same array configuration as the desired configuration of solder balls on the circuit board. A corresponding flux head is used for depositing flux droplets on the array locations of the substrate.
While such techniques are generally effective, they present a number of challenges to the design of fast and efficient apparatus for the placement of solder balls and flux droplets in the context of a real-life production system. The apparatus must be designed so that the ball pick head and the flux head are brought in turn to a position over the substrate, and since the dimensions of the array and in particular the spacing between solder ball locations on the array is small, accurate alignment techniques must be employed. The need in a production process to transfer BGA substrates between locations, and to accurately align ball and flux pick heads over the substrate, presents challenges to the design of a fast and efficient apparatus.
According to the invention there is provided apparatus for placing at least two elements on a surface, comprising:
(a) means for supplying a said surface, said supplying means being adapted to move in a first direction,
(b) first transferring means for transferring a said first element to said surface,
(c) second transferring means for transferring a said second element to said surface,
(d) means provided on at least one of said transferring means for recognising and detecting the position of alignment marks on said surface,
(e) means for adjusting the position of said first and second transferring means relative to said surface in response to the position of said alignment marks,
wherein said first and second transferring means are fixed together at a single position in said first direction and means are provided to move said first and second transferring means independently of each other in a second direction transverse to said first direction.
In a preferred embodiment of the invention said first and second transferring means are moved in said second direction to a position over said surface, and means are provided for moving said first and second transferring means in a third direction normal to the said surface. Preferably each said transferring means is provided with a respective recognising means, and means are provided to move each said recognising means with respect to each said transferring means in said first direction. Each said recognising means may comprise a camera assembly. Additionally, preferably means are provided for adjusting the position of the surface in the first direction
Each said transferring means may be adapted to move in the second direction between a first position in which said transferring means receives an element to be placed, and a second position in which said transferring means is positioned above the surface. Each said transferring means may be adapted to transfer a plurality of elements, which elements may be disposed in a desired configuration. The apparatus is particularly suitable for transferring flux droplets and solder balls to a BGA substrate.
Viewed from another broad aspect the present invention provides apparatus for placing flux droplets and solder balls on a ball grid array substrate, comprising:
(a) means for supplying and supporting said substrate, said supplying means being adapted to move in a first direction,
(b) first transferring means for transferring flux droplets to said surface,
(c) second transferring means for transferring solder balls to said surface,
(d) means provided on at least one of said transferring means for recognising and detecting the position of alignment marks on said substrate,
(e) means for adjusting the position of said first and second transferring means relative to said substrate in response to the position of said alignment marks, wherein said first and second transferring means are fixed together at a single position in said first direction and means are provided to move said first and second transferring means independently of each other in a second direction transverse to said first direction, and
(f) means for adjusting the position of each said recognising means with respect to each said transferring means in said first direction.
Viewed from a still further broad aspect the present invention provides a method for placing at least two elements on a surface, comprising:
(a) supplying a said surface in a first direction to a receiving position,
(b) transferring a said first element to said surface by moving a first transferring means in a second direction transverse to said first direction to overly said surface,
(c) transferring a second element to said surface by moving a second transferring means in said second direction transverse to said first direction to overly said surface,
(d) recognising and detecting the position of alignment marks on said surface,
(e) adjusting the position of said first and second transferring means relative to said surface in response to the position of said alignment marks,
(f) moving said first transferring means in a third direction normal to said surface, and
(g) moving said second transferring means in said third direction normal to said surface.
Preferably the positions of the transferring means may be adjusted as required in the second direction and in a rotary direction about an axis parallel to said third direction. The position of the surface may be adjusted in the first direction.
Preferably step (d) is performed by recognising means provided on at least one of the transferring means.
For example, the recognising means may be provided on only one of the transferring means and step (d) may be performed by moving one of said transferring means in said second direction until said recognising means provided on said transferring means identifies a first alignment mark on the surface, moving said one said transferring means further in said second direction and moving said recognising means in said first direction relative to said transferring means until a second alignment mark is identified.
Alternatively recognising means may be provided on both of the transferring means and step (d) may be performed by prepositioning in the first direction the recognising means formed on said first transferring means and moving said first transferring means in the second direction until the recognising means of the first transferring means identifies a first alignment mark on the surface, and prepositioning in the first direction the recognising means formed on said second transferring means and moving said second transferring means in the second direction until the recognising means of the second transferring means identifies a second alignment mark on the surface.
This method is particularly suitable for placing solder balls and flux droplets on a BGA substrate.